The purpose of this study is to investigate whether naloxone challenge precipitates signs and symptoms of withdrawal in nicotine dependent subjects consistent with that typically observed in naloxone precipitated withdrawal in opiate dependent individuals. So far, two (2) smokers and two (2) nonsmokers participated. We plan to continue recruiting alcohol and nicotine, dependent and non-dependent, subjects until we have ten (10) subjects in each group, at which time all data will be analyzed.